This invention relates to difunctional phosphorus-based gelling agents and gelled nonaqueous treatment fluids, and methods of their use and preparation.
Gelled treatment fluids can be used in a variety of applications requiring a viscous fluid. Some examples include pipeline cleaning applications and subterranean applications, like drilling a well bore in a subterranean formation, stimulating a portion of a subterranean formation, or cleaning a well bore in a subterranean formation, as well as for numerous other purposes. As used herein, the term “treatment fluid” generically refers to a fluid and does not imply any particular action or treatment by the fluid.
Gelled liquid hydrocarbon treatment fluids have been utilized in treating subterranean formations penetrated by well bores, e.g., for stimulation or sand control treatments such as fracturing or gravel packing, respectively. In fracturing treatments, a gelled liquid hydrocarbon fracturing fluid that may comprise particulates, often referred to as proppant, suspended therein is pumped through a well bore into a subterranean formation at a rate and pressure such that one or more fractures are formed or enhanced in a portion of the formation. Proppant particulates may be deposited in the fractures, inter alia, to prevent the formed fractures from closing, thereby maintaining conductive channels through which produced fluids can flow to the well bore. At a desired time, the viscosity of the gelled liquid hydrocarbon fracturing fluid may be reduced, or “broken,” and the fluid may be recovered.
Similarly, sand control operations, such as gravel packing, use gelled liquid hydrocarbon treatment fluids, often referred to as gravel pack fluids. Gravel pack fluids usually are used to suspend gravel particulates for delivery to a desired area in a well bore, e.g., near unconsolidated or weakly consolidated formation particulates, to form a gravel pack to enhance sand control. One common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the annulus between the screen and the well bore with gravel of a specific size designed to prevent the passage of formation sand. The gravel, inter alia, acts to prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the production tubing. Once the gravel pack is substantially in place, the viscosity of the gravel pack fluid often is reduced to allow it to be recovered or produced back from the well bore.
Polyvalent metal salts of orthophosphoric acid esters have been utilized as gelling agents for forming high-viscosity gelled liquid hydrocarbon treatment fluids. Descriptions of such high-viscosity gelled liquid hydrocarbon treatment fluids and methods of their use are set forth, at least in part, in U.S. Pat. No. 4,622,155, issued to Harris et al. on Nov. 11, 1986, and U.S. Pat. No. 5,846,915, issued to Smith et al. on Dec. 8, 1998.
While gelling agents containing polyvalent metal salts of orthophosphoric acid esters have been used successfully in some instances, problems in downstream processes have been encountered. For example, plugging of refinery towers (which often process hydrocarbons produced from formations treated with gelled liquid hydrocarbon fracturing fluids) has caused many expensive, unplanned shutdowns of those towers. The plugging material is high in phosphorus and has been attributed to the phosphoric acid ester gelling agents. Another problem associated with conventional orthophosphoric acid ester gelling agents is that they are not useful to gel fluids that are nonaqueous but not simple hydrocarbons. Such fluids include polar fluids, such as esters, and hydrogen-bonding fluids, such as alcohols. Having the ability to gel such fluids would be desirable, for example, for well bore and pipeline chemical cleanup operations.